The main objective of this proposal is to utilize the ileal mucosa in order to elucidate the mechanisms of action of enkephalins and other neuropeptides. The actions of various neuropeptides on ion transport across this tissue will be measured in vitro using Ussing chambers. Electrical measurements and radioisotope transport studies will be performed. In addition, the effect of the production of tolerance to opiates and the induction of precipitated withdrawal on ion transport will be ascertained. Further investigations will utilize isolated ileal epithelial cells in receptor binding assays to label receptors for opioids, other neuropeptides, serotonin and alpha-adrenergic agents. The action of these agents on cellular concentrations of cyclic nucleotides and cellular calcium fluxes will also be measured and correlated with receptor binding and physiological data. The neuropeptide neurotensin (NT) and the biogenic amine serotonin (5-HT) are found in endocrine cells in the mucosa. The release of these substances from the mucosa will be measured. Investigations will also be made as to the neuronal, endocrine and nutritional factors which control the release of NT and 5-HT. We shall also study the neurotransmitters normally involved in the neuronal regulation of intestinal secretion. These experiments will provide information relating to the mechanisms of action of several neuropeptides and also the physiologfical control of intestinal secretion.